PCSM-Based Energy Storage Devices and Methods

ABSTRACT

Devices and methods for using phase-change-materials to store and retrieve energy. Specifically, the invention discloses various containment devices that may be used to enclose a mass of phase-change-material. The disclosure describes ways it which these devices may be manufactured and ways in which they may be used. The storage devices preferably create an enclosed volume that eliminates any mixing between the phase-change material and any surrounding material such as thermal oil. Further, the invention minimizes the inclusion of unwanted materials such as air.

CROSS-REFERENCES TO RELATED APPLICATIONS

This non-provisional patent application claims the benefit, pursuant to 37 C.F.R. §1.53, of an earlier-filed provisional patent application. The provisional application listed the same inventor. It was filed on 8 Jan. 2015 and was assigned Ser. No. 62/101,065.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of energy. More specifically, the invention comprises devices and methods for using phase-change materials for storing and releasing thermal energy, along with some systems configured to use such a storage and release methodology.

2. Description of the Related Art

Traditional prime-mover-based power generating plants are able to generate electricity in a steady state over long periods of time. Hydroelectric plants do undergo same seasonal variation depending on rainfall but nuclear and coal-fired plants remain on-line nearly continuously.

Solar and wind power based generating systems are now being integrated into the electrical grid. These newer and “greener” systems do not have the luxury of continuous generation. Wind is variable and solar power is by its very nature only available for part of the day. In some periods these systems are able to generate power beyond what is needed on the grid and in other periods there is a shortfall. An efficient means of storing energy produced by wind, solar, and other systems is desirable so that off-peak capacity can be stored and fed onto the grid when it is needed. Unfortunately, effective storage of excess production capacity has not yet been realized.

One prior art approach involves using excess electrical power to pump water into an elevated reservoir during off-peak hours. The available head is then used to drive a turbine to generate additional power in times of increased demand. While this approach does work, it requires the presence of suitable high terrain for the construction of an elevated reservoir. Much of the earth's surface is unsuitable, thereby limiting the use of the reservoir storage technique.

It is also known to use excess production capacity to heat a thermal reservoir containing either a solid (such as concrete) or a liquid (such as thermal oil). This “thermal banking” approach is not dependent on the available terrain features and is therefore more flexible. Unfortunately, however, it is not very efficient. Recovery efficiency is inherently limited when the energy is stored by simply changing the temperature of an available storage mass (a storage system based on sensible heat).

One reason for the inefficiency of the prior art systems is the fact that a large temperature differential must generally be used between the temperature at which energy is added and the temperature at which energy is extracted. For example, superheated steam at 400 degrees centigrade may be used to raise the temperature of a solid energy storage unit from 20 degrees centigrade to 100 degrees centigrade. The elevated temperature in the storage unit may then be used to drive a low-temperature heat engine. The reader will note in this example, however, that there is a large temperature difference between the input and output temperatures. The input temperature of the working fluid used to carry energy into the reservoir is 400 degrees centigrade. The output temperature of a working fluid used to carry the energy back out must be less than the temperature of the reservoir itself, or less than 100 degrees centigrade. This difference generally requires the use of different working fluids and different types of heat engines for adding the energy versus retrieving the energy.

Those working in the field have recognized the fact that changing the phase of the energy-storage medium would offer advantages (a storage system based on latent heat). For example, the phase of a solid storage medium can be changed by raising the temperature to its melting point. Considerable energy is absorbed in the phase change. Conversely, if a working fluid is later used to extract heat and again solidify the storage medium then an efficient retrieval of the energy is possible. And, the difference in temperature between the heat-adding versus the heat-removing cycles can be very low. The heat-adding cycle can use a working fluid that is heated just above the melting temperature of the storage medium. The heat-removing cycle can use a working fluid that is just below the melting temperature. The difference between the input and output temperatures may be as little as 10 degrees centigrade. The same heat engine may be used for adding energy and removing energy, and the same working fluid can be used.

A suitable “phase-change thermal storage medium” should be selected for use in the inventive system. The term “phase-change thermal storage medium” means a substance that changes phase from a solid to a liquid at an appropriate temperature or range of temperatures for use in a heat storage and retrieval system. In the retrieval phase the thermal energy will generally be used to drive some type of heat engine. The solid-to-liquid transition temperature must therefore be above 100 degrees centigrade and preferably much higher. There are several ways that this can be achieved. The phase-change material can be either a single chemical such as a salt, or a mixture of phase-change materials known as a “eutectic.” The word “eutectic” in its narrowest sense means a mixture of substances (at a set ratio) that melts at a single temperature that is lower than the melting points of the separate constituents. In a broader sense the word “eutectic” is used to mean a phase-change material that has a common melting point at a specific mixture (the “eutectic point”) but that may also be used at different mixtures to produce other desirable melting temperature ranges. These other mixture ratios are said to be “hypoeutectic” or “hypereutectic.”

Thus, by combining various chemicals in the correct mixture ratio, the eutectic can be tailored to change its phase at a specific range of temperatures. This combination can be designed to match a particular heat source.

Although the characteristics of a eutectic are known to those knowledgeable in the field of heat transfer and storage, some additional explanation may still be helpful. This is particularly true since the word “eutectic” may have a different meaning in different contexts. A “eutectic” material is generally a mixture of two different substances (though smaller amounts of other substances may be present as well). At one specific mixture ratio, the mixture of the two substances (when in a liquid state) will form a single, unified melting/solidification temperature. As stated previously, this specific mixture ratio is often called the “eutectic point.” For such a ratio, if the molten mixture is slowly cooled it will transition to a uniform solid at a single transition temperature.

If a mixture ratio that is different from the “eutectic point” is used, then the molten mixture will not transition to a uniform solid at a single temperature. Instead, one of the two major mixture constituents will solidity first and the second constituent will solidify at a lower temperature. This is usually referred to as a first “phase” solidifying before the other (from the fact that the physical characteristics are often plotted on a phase diagram).

The use of a mixture ratio that is different from the eutectic point may provide some advantages in certain applications. This is true because the overall transition from one phase to another can take place over a range of temperatures rather than a single temperature. Thus, while a eutectic may be used in the present invention and is in fact preferred, this does not mean that the eutectic will have the exact mixture ratio needed to create a single liquid/solid transition temperature.

While eutectic materials offer advantages in the field of thermal storage, other simple materials may serve in some applications and may be used in the present invention as well. A simple (non-eutectic) example of a phase-change storage medium is sodium chloride, commonly known as “table salt.” Sodium chloride melts at 801 degrees centigrade (1,474 degrees Fahrenheit). Thus, with sodium chloride, a high-temperature working fluid can be used for both the introduction of energy and the subsequent extraction of energy

It is known in the art to use sodium chloride capsules immersed in a high-temperature thermal oil to store thermal energy. The oil receives the input thermal energy and transmits it to the salt capsules. Exemplary embodiments of this approach are described in the following publications: WO2014/100096A1, US2013/0192792A1, US2013/0105106A1, US2014/0197355A1, and US2013/0104546.

Sodium chloride is by no means the only substance that can be used for this process and in fact many other compounds are known to work. Sodium chloride is quite common and inexpensive, however, so it certainly represents a workable though not generally optimal approach. A eutectic provides more flexibility. It can be made up of a combination of chemicals providing a unique melting temperature or range of temperatures that is particularly suited for a specific energy storage and retrieval scenario. Throughout the balance of this disclosure, wherever the phrase “phase-change storage medium” is used without qualification, the reader should understand that the meaning is preferably a eutectic but possibly other suitable materials as well (including simple material such as sodium chloride). The acronym “PCSM” will be used for “phase-change storage medium.”

A typical manufacturing process is to take pre-molded PCSM volumes and encapsulate them in a heat-resistant flexible membrane. The PCSM in the capsule is then melted. Solid PCSM materials often assume the form of crystalline grains. Air that was trapped in the voids between the PCSM grains is expelled through the membrane.

The expulsion of the air and the varying volume of most PCSM materials are known and significant problems. For example, the density of liquid sodium chloride is far less than solid sodium chloride. Solid sodium chloride has a specific gravity of 2.165 whereas liquid sodium chloride has a specific gravity of only 1.556. A similar difference exists for most all PCSM's, including most if not all eutectics. This difference is significant for an entrapped volume. An entrapped volume contains a fixed mass of PCSM. When this melts, the much lower density will increase the pressure within the containment. Conversely, when liquid PCSM re-solidifies the volume of the PCSM is greatly reduced.

If a “blob” of liquid PCSM is contained within a surrounding thermal oil and it is cooled below its melting temperature, the outer surface cools first and forms a shell like the shell of an egg. It is not unusual for a solid exterior and liquid interior to remain for some period. This is particularly true for most eutectics, which tend to have a low thermal conductivity when they solidify into a crystalline form. Once formed, the solid shell becomes an insulator.

As more and more heat is removed the PCSM sets and shrinks further. Eventually a void in the center of the mass forms. A vacuum is created in the void, and this vacuum may become quite strong. The opposite phenomena occur when the mass is again melted. One may readily perceive from this explanation that considerable mechanical stress is placed on each volume of PCSM in successive melt and “freeze” cycles.

It is known to electroplate the outer skin of a PCSM volume with a metal to create a non-melting barrier. This barrier helps to segregate the PCSM from a surrounding medium (such as thermal oil) and mechanically reinforces the volume as well. The metal layer is quite thin, however, and it does not tend to last very long.

The present invention provides improved devices for containing PCSM that is to be used in phase-change-based energy storage and retrieval devices. Methods for manufacturing and using the devices are disclosed. The present invention also provides operational storage and recovery systems configured to use the improved storage devices.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention comprises devices and methods for using phase-change thermal storage materials to store and retrieve energy. Specifically, the invention discloses various containment devices that may be used to enclose a mass of phase-change-material. The disclosure describes ways in which these devices may be manufactured and ways in which they may be used in storage and recovery systems.

The storage devices preferably create an enclosed volume that eliminates any mixing between the phase-change storage media and any surrounding material such as thermal oil. Further, the invention minimizes the inclusion of unwanted materials such as air.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view, showing a containment vessel made according to the present invention.

FIG. 2 is a sectional perspective view, showing interior details of the vessel from FIG. 1.

FIG. 3 is a sectional perspective view, showing one method of creating an end-seal in the vessel.

FIG. 4 is a sectional perspective view, showing the creation of an end-seal.

FIG. 5 is a sectional perspective view, showing the completion of the solidification process from FIG. 4.

FIG. 6 is a sectional perspective view, showing the creation of a flat end on the solidified PCSM in the vessel.

FIG. 7 is a sectional perspective view, showing the addition of a sealing cap over the flat end created in FIG. 6.

FIG. 8 is a sectional perspective view, showing another embodiment in which a vent tube is used to vent interior gas.

FIG. 9 is a sectional perspective view, showing the operation of the embodiment of FIG. 8.

FIG. 10 is a sectional perspective view, showing the use of a vent cap to seal the vent in the embodiment of FIG. 8.

FIG. 11 is a sectional perspective view, showing the completion of the solidification process for the embodiment of FIG. 8.

FIG. 12 is a sectional perspective view, showing an alternate shape for the containment vessel.

FIG. 13 is a perspective view, showing an elongated vessel made according to the present invention.

FIG. 14 is a perspective view with a cutaway, showing an exemplary construction for a thermal energy storage battery made according to the present invention.

FIG. 15 is a perspective view, showing an assembly of multiple thermal energy storage batteries.

FIG. 16 is an elevation view, showing some exemplary features for a thermal energy storage battery.

FIG. 17 is an elevation view, showing a thermal energy storage battery incorporating a resistive heating bank.

FIG. 18 is a schematic view, showing the use of a thermal energy storage battery to drive a heat engine.

FIG. 19 is a schematic view, showing the use of a thermal energy storage battery with various recovery devices.

FIG. 20 is a sectional view, showing an arrangement for transferring energy from a gas flue into a thermal energy storage battery.

FIG. 21 is a schematic view, showing the use of a thermal energy storage battery to mitigate voltage fluctuations on a power distribution grid.

FIG. 22 is a plot showing how the system of FIG. 21 can be switched between the energy generation mode and the energy storage mode on the basis of grid voltage.

REFERENCE NUMERALS IN THE DRAWINGS

10 vessel

12 side wall

14 closed end

16 open end

18 interior

20 cooling medium

22 liquid PCSM

24 solid PCSM

26 void

28 PCSM bulkhead

30 end flat

32 cap

34 fillet weld

36 vent tube

38 interior vent opening

40 gas

42 exterior vent opening

43 fillet weld

44 vent cap

46 thread

48 end wall

50 hemisphere

52 flange

54 elongated vessel

56 cylindrical side wall

58 hemispherical end cap

60 manufacturing feature

62 thermal energy storage battery (“TESB”)

64 input pipe

66 output pipe

68 housing

70 input pipe exit

72 baffle

74 output pipe entrance

76 input header

78 output header

80 circulation pump

82 evaporator

84 heat exchanger

86 working fluid input

88 working fluid output

90 resistance heating bank

92 turbine

94 generator

96 condenser

98 pump

100 flue

102 TESB

104 heat exchanger

106 turbine

108 generator

110 condenser

112 pump

114 pump

116 back pressure turbine

118 heat exchanger

120 turbine

122 generator

124 condenser

126 pump

128 pump

130 thermal oil

132 gas flue passage

134 phase voltage

136 inverter

138 IGBT inverter

140 distribution grid

142 resistance heating bank

144 pump

146 evaporator

148 ORC circulation loop

150 pump

152 condenser

154 turbine

156 3-phase generator

158 rectifier

160 DC bus

162 IGBT shunting module

164 IGBT inverter module

177 mode of operation

178 wind power

180 solar power

182 power stabilization system

DETAILED DESCRIPTION Of THE INVENTION

The invention uses various containment vessels to contain the phase-change-material in use. Sodium chloride is a preferred phase-change-material and it will be used in the descriptions of the inventive embodiments. However, the reader should bear in mind that the invention is by no means limited to this one material.

FIG. 1 shows vessel 10. A cylindrical side wall 12 defines open end 16. FIG. 2 shows a sectional view of the same vessel 10. Closed end 14 defines the bottom of the vessel in the orientation shown in the view. The combination of side wall 12 and closed end 14 create an enclosed interior 18. The enclosed interior is used to contain the PCSM, such as a eutectic.

The general concept of the invention is that vessel 10 will contain the PCSM and segregate the PCSM from a surrounding heat-transfer medium. For example, a multitude of PCSM-containing vessels may be immersed in a high-temperature thermal oil. The vessels are actually immersed in the oil (not on the surface but distributed throughout the oil). Heat that is transferred to or from the thermal oil is transferred to or from each of the vessels in the oil.

It is obviously desirable to provide each PCSM-containing vessel with a long service life. In order to achieve this goal, it is preferable to seal the PCSM within the vessel so that it cannot mix with the surrounding thermal oil. Thus, the creation of a sealed PCSM-containing vessel is one objective of the invention. There are various ways to accomplish this goal.

One approach is to load vessel 10 with liquid PCSM and then seal it somehow. FIG. 3 shows the vessel loaded with liquid PCSM 22. This operation is obviously performed above the melting temperature of the PCSM (such as above 801 degrees centigrade for sodium chloride). The material used for the vessel must be able to withstand this temperature without degrading. It must also be able to withstand considerable mechanical stress—as will be explained subsequently. High-carbon steel is one suitable choice for the wall material. Other alloys—such as chromium—may be added for corrosion resistance or other desired properties.

Even with the use of chromium steel for the vessel, the temperature needed to melt the PCSM can cause unwanted oxidation and other changes. In order to minimize these effects, one may wish to carry out the PCSM filling and melting operations in an inert atmosphere. As an example, one could perform the filling and melting operations in an argon or nitrogen atmosphere.

Once the filling operation is completed, the liquid PCSM is cooled near the open end of the container. Cooling median 20 is applied to the open end and heat flows out of the liquid PCSM in that area. The term “cooling medium” is intended to encompass a wide variety of cooling devices and techniques, including:

1. Applying a cooler heat sink—such as a clamped on collar of steel (a close sliding fit at a lower temperature—such as 500 degrees centigrade—that expands and becomes loose as the collar heats);

2. Applying a jacket with a circulating cooling fluid (such as liquid sodium); and

3. Applying a blast of cold argon.

Alternatively, one could continue applying heat to the bottom of the vessel (closed end 14) and simply remove the heat from the top so that a differential cooling rate develops. In any event, the desire is to solidify the liquid PCSM proximate the container's open end while the rest remains liquid.

FIG. 4 shows the result. A “bulkhead” of solid PCSM 24 has formed over the end while liquid PCSM 22 remains. Solid PCSM 24 seals the open top of the vessel. The remaining liquid PCSM is then allowed to cool and solidify. This operation preferably occurs relatively slowly in order to avoid placing too much stress on the solid PCSM at the top of the vessel.

FIG. 5 shows the same vessel after all the PCSM has solidified. The reader will note the creation of void 26 in the center of the mass. This void is created as the PCSM solidifies because the density of solid PCSM is typically so much higher than that of liquid PCSM. The location and shape of the void is somewhat variable, but the location shown is usually expected. This is true because the heat transfer from the liquid PCSM commences at the walls of the vessel and a shell of solid PCSM is formed at that point. This shell is mechanically strong and it does not tend to collapse inward.

Void 26 is an evacuated space so a vacuum within, the container is actually created. PCSM bulkhead 28 most be strong enough to resist the collapsing force created by the vacuum within void 26. Likewise, the vessel walls must be strong enough to resist the collapsing force.

The PCSM bulkhead is only a temporary solution to the problem of sealing the vessel. The reader will recall that the PCSM within the vessel is to be melted and solidified regularly. Thus, the PCSM bulkhead will not survive the next melting cycle. FIGS. 6 and 7 illustrate one solution to the problem of creating a permanent seal.

In FIG. 6, end flat 30 has been created by cutting, grinding, or otherwise removing material. It may in some cases be difficult to create the flat without weakening the PCSM bulkhead across the end. Thus, it may be desirable to create a removable end section of the vessel side wall so that the material of the side wall itself does not have to be cut or ground.

Once end flat 30 is created, it must be sealed. FIG. 7 shows the placement of cap 32 over the open end. Cap 32 may be made of high-carbon steel as for the balance of the vessel. Once it is in position fillet weld 34 is run around the perimeter to join the cap to the side wall. The result is a sealed vessel with very little entrapped gas. The small amount of gas (trapped between the flat and the underside of the cap) may be an inert gas in order to minimize corrosive effects.

The cylindrical side wall and end caps create a pressure-tight containment completely enclosing an enclosed volume. The phase-change thermal storage medium occupies substantially all of the enclosed volume. The phrase “substantially all” means that the storage medium fills greater than 50%—and preferably greater than 75%—of the enclosed volume while in the liquid state.

Rather than using a cap one could provide a flat plate that sits directly on top of the ground end flat 30. By making the ground surface flat and smooth and making the plate a close fit one may prevent unwanted gas remaining with the vessel volume.

One could elect to install the cap directly on the open end of the vessel in the state shown in FIG. 5. This would entrap a significant volume of gas within the vessel. A suitable design can accommodate the entrapped gas, but it does have disadvantages. The entrapped gas will be heated to a very high temperature when the PCSM Is melted. This will create significant pressure. An alternative approach is to evacuate some of the ambient gas when the vessel is in the state shown in FIG. 5 and to add the fillet weld under the same low-pressure state. This will reduce the mass of entrapped gas. However, welding in a semi-vacuum atmosphere has its challenges. Many conventional processes do not work well because of the lack of suitable gap conductivity (arc processes). It may be preferable to use contact welding.

Other embodiments may be devised to eliminate the need for a large welding operation to seal the vessel. FIGS. 8-11 illustrate some embodiments that avoid the need to seal the open end of the vessel. In the embodiment of FIG. 8, the vessel has been loaded with solid PCSM 24. However, the reader should realize that the solid PCSM shown comprises densely-packed PCSM grains rather than PCSM that has been solidified from a “melt.” This PCSM can simply be poured in the open top of the container (at room temperature) before cap 32 is welded in place.

Vent tube 36 is provided in the vessel. It is sealed to the lower end of the vessel using fillet weld 43 or some other suitable joining method. Vent tube 36 provides an unimpeded passage between the vessels's interior and exterior. Interior vent opening 38 is placed near the top of the vessel (in the orientation of the view). Exterior vent opening 42 is placed at any convenient location.

Vent tube 36 is preferably attached in place with the top of the vessel still open (before cap 32 is added). Crystalline PCSM is then poured in. A suitable amount is added so that the vessel will be filled by the volume of liquid PCSM created during the melting process. Cap 32 is welded in place to seal the vessel. A volume of gas 40 (which may be an inert gas) is present. An additional volume of gas exists in the voids between the grains of PCSM.

FIG. 9 shows the initial melting process applied to the embodiment of FIG. 8. Heat is added to melt the PCSM. In the state shown, melting pieces of solid PCSM 24 are circulating in the accumulating volume of liquid PCSM 22. Gas 40 is forced out through vent tube 36 as the volume within the vessel increases (owing to the transition of solid PCSM to liquid PCSM).

In FIG. 10 the mass of PCSM within the vessel has melted completely to form a reservoir of liquid PCSM 22. At this point the vent tube is preferably sealed. The vent tube may be sealed by a wide variety of methods, including welding, brazing, and capping. In the embodiment of FIG. 10, thread 46 is provided on the exterior surface of the vent tube. Vent cap 44 is threaded over the vent tube to seal the tube. It is likely that vent cap 44 will remain in this position for the useful life of the filled vessel. Thus, adhesive or other sealing agents may be applied to the threaded engagement.

FIG. 11 shows the finished result. Solid PCSM 24 lies within the vessel. A first void 26 lies along the vessel's central axis. A second void 26 likely lies near the top next to the entrance of the vent tube. This second void may contain some unvented gas. Again, this may be an inert gas such as argon.

The assembly of FIG. 11 may be melted and re-solidified many times in an energy storage and retrieval system. It will remain sealed and it will retain the PCSM in a good, usable condition.

It is desirable to minimize the mass of gas entrapped within the sealed vessel. Entrapped gas expands during the melting process and can create substantial unwanted pressure. Accordingly, sealing techniques that reduce or eliminate entrapped gas are preferred. Returning now to FIG. 3, the reader will recall at this point that the vessel is filled with liquid PCSM 22. Rather than applying cooling medium 20, a metal cap or disk can be pressed down into the vessel until it presses into the top of the liquid PCSM. One or more gaps or vents can be provided in the disk to vent the displaced gas. The cap and vessel can then be cleaned up and welded to form a tight seal.

Another approach is to place a disc down into the vessel to the top of the liquid PCSM and then roll-crimp the upstanding lip of sidewall 12 over the top of the disk to secure it in place. This operation is analogous to the roll-crimping operation used to seal a shotgun shell. Either the capping or roll-crimping devices can be pushed far enough into the vessel to displace all the gas and a quantity of liquid PCSM (by displacing some liquid PCSM one may be confident that all the gas has been displaced).

Although a pipe-shaped containment vessel has been illustrated for the preceding embodiments, the invention is by no means limited to any particular shape or form. In fact, other shapes may well be more advantageous and a particular energy-storage system may contain combinations of different shapes in order to control the overall melt rate.

FIG. 12 shows an additional embodiment to illustrate a different shape for the vessel. Vessel 10 in FIG. 12 is spherical. It is created by assembling two hemispheres 50. Each hemisphere 50 is provided with a mating flange 52. The two flanges are joined by welding or brazing to create an enclosed volume.

Vent tube 36 is provided as for the prior examples. The vent tube is sealed to the two hemispheres. PCSM is loaded into the interior and then the assembly is heated to melt the PCSM. Gas within the container is vented through vent tube 36. Once all the PCSM mass is melted. Vent cap 44 is applied to seal the vessel. The vessel is then cooled and solid PCSM 24 forms as shown. One or more internal voids 26 are created as the PCSM solidifies.

FIG. 13 shows still another embodiment for the vessel—designated as elongated vessel 54. This embodiment creates an enclosed volume by joining a cylindrical side wall 56 to a hemispherical end cap 58 on each end. Manufacturing feature 60 represents a feature such as a sealed vent cap that is used during the loading and sealing of elongated vessel 54. Once manufacturing is complete, the manufacturing feature remains sealed. As for the prior examples, the elongated vessel is intended to remain sealed throughout its useful life of storing and releasing thermal energy.

The length of elongated vessel 54 is preferably much greater than its diameter. As an example, then length may be 2 meters while the diameter may only be 5 cm. The use of the hemispherical end caps creates a strong structure that is able to withstand the significant internal vacuum created when the PCSM solidifies. It is also able to withstand any positive pressure created when the PCSM melts. The resulting structure is essentially a long “rod” with a favorable surface-area-to-volume ratio. This favorable ratio assists in the transfer of heat into and out of the vessel.

FIGS. 14 and 15 illustrate a thermal storage device configured to use multiple elongated vessels 54. FIG. 14 shows one embodiment of a thermal energy storage battery 62 (“TESB”). The TESB seeks to store and release thermal energy in a system that is roughly analogous to voltaic cells used to store and release electrical energy.

Housing 68 completely encloses the components contained within its interior so that it can be flooded with a suitable thermal oil. The front and top portions of the housing are cut away in the view to show the internal structures. Multiple elongated vessels are mounted within the TESB's interior. Each of these elongated vessels contains a suitable thermal storage PCSM as described previously. Mounting hardware is provided to suspend the elongated vessels in the orientation shown (with the cylindrical side wall of each vessel being in a vertical orientation). In this particular embodiment multiple baffles 72 perform a dual purpose. Each baffle provides a mounting point for the elongated vessels and also directs the flow of circulating thermal oil.

Input pipe 64 carries in thermal oil and releases it through input pipe exit 70 below the lowest baffle 72. From this point the thermal oil is forced to flow along a serpentine path around a series of baffles 72 until it finally emerges proximate output pipe entrance 74. From there the thermal oil is carried out through output pipe 66.

The thermal oil preferably has a suitable viscosity, good stability, and good thermal conductivity over the range of temperatures to be used. Exemplary thermal oils are listed in the following table, along with some of their physical characteristics:

Volume Con- specific Temperature duct- Thermal thermal Cold (° C.) Hot (° C.) ${Density}\mspace{14mu} \left( \frac{kg}{m^{3}} \right)$ ivity (W/mK) capacity (kJ/kgK) capacity (kWh_(l)/m³) Mineral 200 300   770 0.12 2.6  55 oil Synthetic 250 350   900 0.11 2.3  57 oil Silicone 300 400   900 0.10 2.1  52 oil Nitrite 250 450 1,825 0.57 1.5 152 salts Nitrate 265 565 1,870 0.52 1.6 250 salts Carbonate 450 850 2,100  2.0 1.8 430 salts Liquid 270 530   850 71.0 1.3  80 sodium

The values for “hot” and “cold” temperatures are somewhat subjective. The “cold” temperature represents a circulating temperature of the thermal oil being used when thermal energy is being extracted from the TESB whereas the “hot” temperature represents a circulating temperature when thermal energy is being added to the TESB.

Elongated vessels are arranged in an array within TESB 62 so that suitable passages for the moving thermal oil are provided between each elongated vessel 54 and its neighbors. Each baffle 72 includes a pattern of circular openings to allow the elongated vessels to be placed in position. As one manufacturing option the baffles may be secured in place and the elongated vessels 54 may then be introduced through the open top of housing 68 before the housing is closed and sealed. The elongated vessels and the baffles may then be brazed together. Alternatively, mechanical fasteners may be used to connect some or all of the elongated vessels to the baffles.

The reader will thereby appreciate how the structure of FIG. 14 functions. If the intention is to store thermal energy then an external device is used to send heated thermal oil into and through the TESB in order to raise the temperature of the array of elongated vessels 54 and melt the PCSM contained within the elongated vessels. If the intention is to retrieve thermal energy then a thermal oil at a cooler temperature is passed through the TESB in order to extract heat from elongated vessels 54 until such time as the PCSM within the elongated vessels has solidified.

It is possible to arrange multiple TESB's so that they are connected in parallel or in series (or in combinations thereof) just like electrical batteries. FIG. 15 shows a set of eight TESB's that are connected in parallel. All the input pipes 64 for the eight TESB's are connected to input header 76. Likewise, all the output pipes 66 for the eight TESB's are connected to output header 78. In this way a single input and output conduit can be used for the eight TESB's. It is also possible to arrange the connection of the TESB's in series.

The reader will note that the arrangement in FIG. 15 is long and narrow and aptly configured for mounting on a flat-bed trailer or incorporation into a standard-sized cargo container. An arrangement of TESB's can be used to collect thermal energy at one site and transport it to another location. Of course, suitable insulation is preferably provided in order to increase the storage time. A refractory ceramic layer can be added around an individual TESB as shown in FIG. 14. Alternatively, a single insulating covering can be added around a cluster of TESB's like the one shown in FIG. 15. Assuming that all the TESB's will be operated at the same temperature (often but not always true) a single insulating enclosure can be provided for multiple TESB's.

The applications for the TESB's made according to the present invention are numerous. A few illustrative examples may benefit the readers understanding. However, the reader should at all times bear in mind that the examples provided in FIGS. 16-20 represent a small sample of many other possibilities.

FIG. 16 represents an embodiment where the thermal fluid within the TESB is circulated internally but a separate working fluid is used to add energy to the TESB and still another working fluid is used to extract energy from the TESB. As for the prior examples, the TESB contains an array of multiple elongated vessels 54 and baffles 72. Heat exchanger 84 is provided so that a segregated second working fluid can be passed through the TESB to add thermal energy. This second working fluid circulates to some external heat-generating source (such as a cement manufacturing plant). Circulation pump 80 circulates the thermal oil within the TESB so that the thermal energy being added by heat exchanger 84 is evenly distributed.

The thermal energy stored within the TESB of FIG. 16 may be extracted using still another working fluid. Evaporator 82 is contained within the TESB. It receives the third-type of working fluid through working fluid input 86 and discharges it through working fluid output 88. In this example the working fluid changes from a liquid to a vapor as it passes through evaporator 82. The vapor could then be used to power devices such as a back-pressure turbine or conventional turbine.

Alternatively, heat exchanger 84 could be used to extract thermal energy in addition to adding it. Further, both evaporator 82 and heat exchanger 84 could be used to extract thermal energy when desired. Both could be operated simultaneously, or one or the other could be selected.

FIG. 17 shows another embodiment of TESB 62. In this version energy is transferred into the TESB via resistance heating bank 90. This embodiment is configured to store excess electrical production capacity. When excess capacity exists, it is routed to resistance heating bank 90. Thermal oil is circulated around the TESB by circulation pump 80. The incoming thermal energy melts the solid PCSM within elongated vessels 54.

Energy is retrieved from the embodiment of FIG. 17 via evaporator 82. A separate working fluid is again expanded through evaporator 82 and used to provide mechanical energy to a separate device. The energy extraction cycle may be accomplished in any number of ways. One common way is through the use of a prior art heat engine.

FIG. 18 illustrates a prior art heat engine connected to a single TESB 62. In actuality, a single heat engine might be powered by a bank of many TESB's. However, the operating principles would be the same. A working fluid—such as water—is converted to steam in evaporator 82. The steam is then expanded through turbine 92. Turbine 92 powers generator 94, which produces electricity. The expanded steam next passes through condenser 96. Pump 98 re-pressurizes the working fluid and sends it back to evaporator 82.

If the desire is to feed the energy from the TESB back onto the electrical grid to assist in times of reduced supply, then generator 94 may be equipped with amplitude and phase matching circuitry. Those skilled in the art will appreciate that the overall efficiency of the electrical storage and retrieval cycle for the embodiments of FIGS. 17 and 18 will be modest. However, the storage and return of any electrical energy represents an improvement for many installations. Even modest efficiencies are therefore still worthwhile.

The TESB can be applied in many other configurations apart from the electrical storage scenario. Since the TESB is essentially a “Thermal battery” it may be used to directly store thermal energy. FIG. 19 illustrates this option. An industrial process is expelling very hot flue gas. The process might be a power generation plant, a chemical plant, or a cement manufacturing plant.

TESB 62 is positioned to harvest some of the energy escaping from flue 100. FIG. 20 provides a section view through TESB 62 and 102 shown in FIG. 19. Numerous gas flue passages 132 are interspersed within the array of elongated vessels 54. Thermal oil 130 is circulated within each TESB as for the other embodiments. Thus, the hot gas passing through gas flue passages 132 transfers heat to the thermal oil and the thermal oil transfers heat to elongated vessels 54.

Returning now to FIG. 19, the two TESB's are configured to store thermal energy in a different temperature range. TESB 62 receives hotter flue gas. TESB 102 receives flue gas after it has been cooled somewhat by the lower TESB. Accordingly, different types of heat engines may be used to harvest the thermal energy.

Evaporator 82 removes thermal energy from TESB 62. Back-pressure turbine 116 partially expands the working fluid from evaporator 82—producing some electricity via an associated generator. The partially-expanded working fluid then passes through heat exchanger 118. Pump 128 pressurizes the working fluid and sends it hack to evaporator 82.

Heat exchanger 118 serves as an evaporator for a second circulation loop. In this second loop, a separate working fluid is fully expanded through conventional turbine 120, which powers generator 122. Condenser 124 condenses this working fluid and sends it back to pump 126.

A different configuration is used to extract thermal energy from TESB 102. Pump 114 circulates a liquid working fluid in a loop through TESB 102 and heat exchanger 104. The working fluid in this loop may in fact simply be the thermal oil used in TESB 102 itself.

Heat exchanger 104 is then used as an evaporator for a separate working fluid circulating in a loop through turbine 106, condenser 110, and pump 112. Turbine 106 powers generator 108, which produces electricity.

Different heat engines may be used alone or in combination. For example, one may increase efficiency by using a conventional steam-based heat engine for the initial extraction and then an Organic Rankine Cycle “bottoming” engine to extract additional energy from the “waste heat” portion of the conventional heat engine.

The process depicted in FIG. 19 may not be a continuous one. For example, the heat engine extraction devices may have a low duty cycle (10-50%) while the flue gas may run continuously. The flue gas may have to run for 30 minutes continuously to completely melt all the PCSM within TESB 62. The extraction cycle may then be started for TESB 62. Running the energy extraction cycle may re-solidify ail the thermal storage PCSM in only 10 minutes, at which time the extraction cycle will be shut down and the flue gas will be allowed to re-melt the PCSM within TESB 62.

The question of duty cycle may come into play tor electrical energy storage and retrieval as well. For example, a given grid might have excess capacity for 23 hours of the day and only 1 hour of critical under-supply. The grid might “bank” energy into multiple TESB's for 23 hours of the daily cycle and retrieve energy for only one hour. Even if the overall efficiency of the storage/retrieval cycle was low (say 40%) the use of the TESB's would allow the full demand cycle to be met without having to increase production capacity.

FIGS. 21 and 22 show an additional example of how a TESB can be integrated into a power system. In this example, the primary goal is to mitigate unwanted voltage fluctuation produced by the addition of solar and wind power to a distribution grid. Wind power 178 and solar power 180 feed into inverter 136. Inverter 136 converts the input power to a steady DC voltage. This steady DC voltage feeds IGBT inverter 138. IGBT inverter 138 uses pulse width modulation to synthesize a 3-phase voltage and phase-matched output that is then fed onto distribution grid 140.

In reality many IGBT inverters will be used to feed multiple installations of wind turbines and solar arrays onto distribution grid 140. As explained previously, the variable nature of the wind and solar power can produce grid voltage instability. Oversupply is as common a problem as undersupply. Either causes voltage fluctuations and both are preferably addressed.

Power stabilization system 182 is connected to the same distribution grid 140, though it may be connected in a location that is distant from the locations of the wind and solar power connections. Power stabilization system 182 is intended to both store energy taken from the grid and return energy to the grid. However, its focus is more on improving grid stability than achieving great efficiency in the storage/retrieval cycle.

IGBT inverter module 164 is a bi-direction device in the embodiment shown. It can take DC power available on DC bus 160 and feed it onto distribution grid 140 (after appropriate phase and voltage matching to create an AC feed). It can also take AC power from grid 140 and convert it to stable DC power before feeding it onto DC bus 160.

In periods where too much power Is available on distribution grid 140 (and the grid voltage is consequently running too high) power stabilization system 182 goes into “storage mode.” Inverter module 164 feeds power onto DC bus 160. Rectifier 158 is preferably inactive in this mode. IGBT shunting module 162 feeds the electrical power from DC bus 160 to resistance heating bank 142 in thermal energy storage battery (“TESB”) 102. The heating bank heats the circulating oil and stores energy by melting the phase-change storage medium (“PCSM”) in the TESB.

When the voltage on distribution grid 140 later falls below its nominal value power stabilization system 182 will switch to “generation mode.” Pump 144 at that point begins circulating thermal oil from TESB 102 through evaporator 146. Evaporator 146 heats and vaporizes a second working fluid circulating within Organic Rankine Cycle (“ORC”) circulation loop 148. The ORC vapor is expanded through turbine 154. It then circulates through condenser 152 and back to pump 150.

Turbine 154 powers three-phase generator 156. The output of this generator passes two rectifier 158, which converts the power to stable DC and feeds it onto DC bus 160. IGBT inverter module 164 converts this power into phase and voltage-matched AC and feeds it back onto distribution grid 140. Thus, the power previously stored in TESB 102 during a period of over-supply is fed back onto the grid during a period of under-supply.

FIG. 22 graphically depicts this switching. Phase voltage 134 rises and falls with respect to its nominal value of 480 V. Mode of operation 177 changes between the storage mode and the generation mode as appropriate.

If faster response times are needed it may be desirable to run the ORC circulation loop continuously. This creates a third mode of operation. In that case the Organic Rankine Cycle is run continuously and turbine 154 and generator 156 are run continuously. This scenario may remind the reader of a perpetual motion scheme in that energy is being drawn from the grid to keep the TESB heated while the TESB is being used to power a heat engine that may be feeding power back onto the grid. However, the reader should bear in mind that the goal in this third mode of operation is grid voltage stabilization rather than overall efficiency. The continuous operation of the ORC heat engine allows the rapid switching between the storage and generation mode (as fast as several times per second). Overall efficiency will likely suffer, but overall efficiency in this scenario is not the main goal. Other modes of operation are disclosed in my own pending U.S. patent application Ser. No. 14/720,018, which is hereby incorporated by reference.

Many different PCSM materials can be used in the invention and the invention should not be viewed as being limited to any one type of material. As explained previously, simple salts can be used. However, the preferred embodiments use a eutectic as the PCSM. Preferred eutectics are mixtures containing compounds of sodium, potassium, nitrogen, calcium, and oxygen.

Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Many other shapes and combinations are possible for the vessel. Other storage and retrieval cycles are possible as well. Thus, the scope of the invention should be fixed by the following claims rather than the examples given. 

Having described my invention, I claim:
 1. A thermal energy storage battery comprising: a. a housing; b. a plurality of elongated vessels within said housing, each including, i. a pressure-tight containment completely enclosing an enclosed volume, ii. a phase-change thermal storage medium substantially filling said enclosed volume; c. said plurality of elongated vessels being fixed in position within said housing; d. said housing being flooded with a thermal oil; e. a plurality of baffles located within said housing, said plurality of baffles being configured to force a serpentine flow path for said thermal oil within said housing; f. a thermal energy input configured to selectively allow the input of thermal energy to said thermal oil within said housing; and g. a thermal energy output configured to selectively allow the extraction of thermal energy from said thermal oil within said housing.
 2. A thermal energy storage battery as recited in claim 1, wherein: a. each of said elongated vessels includes a cylindrical side wall; and b. said elongated vessels are oriented so that said cylindrical side walls are vertical.
 3. A thermal energy storage battery as recited in claim 1, wherein: a. said thermal energy input is an input pipe for adding said thermal oil to said housing; and b. said thermal energy output is an output pipe for removing said thermal oil from said housing.
 4. A thermal energy storage battery as recited in claim 1, wherein said thermal energy input is a heat exchanger located in said housing, said heat exchanger configured to circulate a working fluid separate from said thermal oil in said housing.
 5. A thermal energy storage battery as recited in claim 1, wherein said thermal energy input is a resistance heating bank.
 6. A thermal energy storage battery as recited in claim 1, wherein said thermal energy output is an evaporator located at least partly within said housing, said evaporator configured to circulate a working fluid separate from said thermal oil in said housing.
 7. A thermal energy storage battery as recited in claim 4, wherein said heat exchanger is a gas flue.
 8. A thermal energy storage battery as recited in claim 1, wherein said phase-change thermal storage medium is sodium chloride.
 9. A thermal energy storage battery as recited in claim 8, wherein said thermal oil is selected from the group consisting of mineral oil and synthetic oil.
 10. A thermal energy storage battery as recited in claim 1 wherein said working fluid separate from said thermal oil in said housing is steam.
 11. A thermal energy storage battery comprising: a. a housing; b. a plurality of vessels within said housing, each including, i. a pressure-tight containment completely enclosing an enclosed volume, ii. a phase-change thermal storage medium substantially filling said enclosed volume; c. said plurality of vessels being fixed in position within said housing; d. said housing being flooded with a thermal oil; e. a plurality of baffles located within said housing, said plurality of baffles being configured to force a serpentine flow path for said thermal oil within said housing; f. a thermal energy input configured to selectively allow the input of thermal energy to said thermal oil within said housing; and g. a thermal energy output configured to selectively allow the extraction of thermal energy from said thermal oil within said housing.
 12. A thermal energy storage battery as recited in claim 11, wherein: a. each of said vessels includes a cylindrical side wall; and b. said vessels are oriented so that said cylindrical side walls are vertical.
 13. A thermal energy storage battery as recited in claim 11, wherein: a. said thermal energy input is an input pipe for adding said thermal oil to said housing; and b. said thermal energy output is an output pipe for removing said thermal oil from said housing.
 14. A thermal energy storage battery as recited in claim 11, wherein said thermal energy input is a heat exchanger located in said housing, said heat exchanger configured to circulate a working fluid separate from said thermal oil in said housing.
 15. A thermal energy storage battery as recited in claim 11, wherein said thermal energy input is a resistance heating bank.
 16. A thermal energy storage battery as recited in claim 11, wherein said thermal energy output is an evaporator located at least partly within said housing, said evaporator configured to circulate a working fluid separate from said thermal oil in said housing.
 17. A thermal energy storage battery as recited in claim 14, wherein said heat exchanger is a gas flue.
 18. A thermal energy storage battery as recited in claim 11, wherein said phase-change thermal storage medium is sodium chloride.
 19. A thermal energy storage battery as recited in claim 18, wherein said thermal oil is selected from the group consisting of mineral oil and synthetic oil.
 20. A thermal energy storage battery as recited in claim 11 wherein said working fluid separate from said thermal oil in said housing is steam. 